I believe what you probably have extracted is the hydrochloride salt of methylphenidate.
If you wish to smoke these crystals you will need to convert your HCL to freebase.
I don't know for sure how this would be done, but if your crystals are soluble in alcohol i imagine you could just do something like.
Redissolve crystals in alcohol, add a base such as baking soda, or washing soda.
washing soda is a stronger base and may work better. If you cant find washing soda you can simply throw some baking soda in the oven at around 250 or so for an hour until your baking soda (sodium bicarbonate) is reduced to washing soda (sodium carbonate.)
after increasing the alkalinity of your solution i would imagine you just recrystallize and obtain a product that is now smokeable.
as far as what method you should use for smoking i would take a guess that vaporization is your best bet.
If you don't have a meth pipe for vaporizing you can make one pretty easily with the glass tube from a garcia vega cigar and a common propane torch.
I'm sure the interwebs has more info on how to make these vaporizers.
another option is running it off foil/chasing the dragon.
also i took a guess on the required base needed to convert your crystals to freebase form.
i have no idea what factors come into play when selecting the appropriate PH your solution needs to be.
You may need something strong such as sodium hydroxide (lye.)
Then again crack is made with baking soda which is very weak.
Anyways I'll stop rambling about what i don't know. The web definitely has the information i could not provide.
I hope i helped steer you in the right direction.